Field of the Invention
The invention relates to medical devices and, more particularly, to methods and devices for accessing the cardiovascular system.
Description of the Related Art
A wide variety of diagnostic or therapeutic procedures involves the introduction of a device into the vasculature through a percutaneous incision at an access site. Such regions of the vasculature, preferred for access, include both the arteries and veins, typically at peripheral locations in the body. Typical access sites include the jugular vein, the subclavian artery, the subclavian vein, the brachial artery, the femoral arteries and the femoral veins. Techniques commonly known for such vascular access include the Seldinger technique. The Seldinger technique involves using a hollow needle to puncture the skin and gain access to the selected artery or vein. A guidewire is next placed through the hollow needle into the selected region of vasculature. The guidewire may be advanced to a target location in the vasculature, often more than 100 cm away from the access site. The needle is removed and a tapered dilator with a sheath and a central lumen in the dilator is advanced over the guidewire into the vasculature. The dilator is next removed and a guide catheter is advanced through the sheath over the guidewire. The guide catheter can be advanced all the way, or part way, to the target site. The guide catheter, following, or without, removal of the guidewire can be used for directing therapeutic or diagnostic catheters to regions of the vasculature and central circulation, including external and internal structures of the heart. A general objective of access systems, which have been developed for this purpose, is to minimize the cross-sectional area of the access lumen, while maximizing the available space for the diagnostic or therapeutic catheter placement therethrough. These procedures are especially suited for coronary angioplasty, stent placement, cerebrovascular coil placement, diagnostic cardiac catheterization, and the like.
Electrophysiology (EP) mapping and cardiac tissue ablation procedures are examples of diagnostic or therapeutic interventional procedures that are commonly performed on the heart. The procedure involves the steps of inserting a hollow needle, with a hemostasis valve affixed to its proximal end, into the femoral vein via a percutaneous puncture. A guidewire is next inserted through the hemostasis valve and the central lumen of the needle into the femoral vein. The guidewire is routed, under fluoroscopic control, cranially toward the heart until it reaches the right atrium via the inferior vena cava. The hollow needle is removed and a sheath with a tapered tip central obturator further including a central guidewire lumen, termed a dilator, is routed over the guidewire, through the skin puncture, through the wall of the femoral vein, and into the central lumen of the femoral vein. The central obturator or dilator is next removed. A Mullins catheter is next routed through the sheath, over the guidewire, and advanced to the right atrium. The guidewire is removed and a Brockenbrough™ (Trademark of C.R. Bard, Inc.)—type needle is inserted through the proximal end of the Mullins™ catheter and routed to the right atrium. The Mullins catheter is positioned, under fluoroscopic guidance, so that its distal end is located in the Foramenal valley, a feature in the septal wall of myocardium that divides the right atrium from the left atrium. The Foramenal valley is the remains of a communication between the right and left atrium, which exists prior to birth, but which closes following birth due to the pressures imposed by the beating heart of the newborn infant. The Brockenbrough needle is next advanced through the atrial septum in the general region of the Foramenal valley. The Mullins catheter is next advanced over the Brockenbrough needle until its distal end resides within the left atrium. Hemostatic valves at the proximal end of all hollow devices permit sealing around catheters and devices inserted therethrough with corresponding prevention or minimization of blood loss and the entry of air.
The procedure continues with the Brockenbrough needle being withdrawn and replaced with a 0.032 to 0.038 inch diameter guidewire, generally of the stiff variety. This guidewire may have a bifurcated distal end to prevent inadvertent retraction once the guidewire has been advanced and expanded into the left atrium. The Mullins catheter is next withdrawn and replaced with a guide catheter having internal dimensions generally around 8 French and a tapered, removable obturator. The guide catheter is advanced into the right atrium and across the atrial septum, following which the obturator is removed. At this time, diagnostic and therapeutic catheters can be advanced into the left atrium so that appropriate EP mapping and ablation can occur. However, problems sometime arise, when trying to pass the guide catheter across the atrial septum, in that the tract generated by the Brockenbrough needle and Mullins catheter closes too tightly to allow passage of the guide catheter. At this point, a balloon catheter is advanced over the guidewire and through the guide catheter. The balloon catheter is advanced so that its dilatation balloon traverses the atrial septum. The balloon catheter is next inflated to stretch the tissues surrounding the atrial septal puncture. At this time, the guide catheter can have its dilator re-inserted and the entire assembly advanced over the guidewire through the atrial septum and into the left atrium.
Current therapeutic techniques may involve advancing an EP mapping catheter through the guide catheter and positioning the EP mapping catheter at various locations within the left atrium. Electrocardiogram signals are sensed by the EP mapping catheter. These signals are conducted or transmitted from the distal tip to the proximal end over electrical lines routed along the length of the EP catheter. The signals are analyzed by equipment electrically connected to the proximal end of the EP mapping catheter. Catheter guidance is generally accomplished using X-ray fluoroscopy, ultrasound imaging such as ICE, TEE, and the like. Therapy generally involves radio-frequency (RF) electromagnetic wave generation by external equipment electrically connected to an EP therapeutic catheter. The EP therapeutic catheter is advanced into the left atrium into regions of foci of electrical interference of the hearts normal electrical conduction. Application of such radio-frequency energy at the tip of the EP therapeutic catheter, which is brought into contact with the myocardium, causes tissue ablation and the elimination of the sources of these spurious signals or re-entry waveforms. A primary area targeted for RF tissue ablation is the area surrounding the origin of the pulmonary veins. Often a ring-type electrode is beneficial in performing this procedure. Such tissue ablation can be performed using RF energy to generate heat, but it can also be performed using microwaves, Ohmic heating, high-intensity focused ultrasound (HIFU), or even cryogenic cooling. The cryogenic cooling may have certain advantages relative to heating methodologies in that tissue damage is lessened. Although a single atrial septal puncture may be adequate for electrophysiological mapping of the left atrium, therapeutic systems, including RF ablation devices often require that two atrial septal punctures be performed. A risk of atrial septal punctures includes potentially perforating the aorta, a high-pressure outlet line, which resides quite close to the atrial septum.
Provision is generally made to deflect instrumentation through substantial angles, between 20 and 90 degrees, within the right atrium to gain access to the atrial septum from a catheter routed cranially within the inferior vena cava. To address this situation, the Brockenbrough needle, the Mullins catheter, or both, are substantially curved and significant skill is required, on the part of the cardiologist or electrophysiologist to negotiate the path to the atrial septum and into the left atrium.
One of the primary issues that arise during electrophysiology procedures in the heart is the need to remove and replace multiple instruments multiple times, which is highly expensive and adds substantial time to the conduct of the procedure. A reduction in the number of catheter and guidewire passes and interchanges would reduce procedure time, reduce the risk of complications, improve patient outcomes, reduce procedural cost, and increase the number of cases that could be performed at a given catheterization lab. Current procedures involving multiple atrial septal penetrations would be reduced in frequency or become less time consuming and less risky if only a single atrial septal penetration was necessary. Additional benefit could be derived if larger catheters could be used, thus enabling the use of more sophisticated, powerful, and accurate instruments to improve patient outcomes. The limitations of current systems are accepted by physicians but the need for improved instrumentation is clear. Furthermore, placement of implants within the left atrium, such as the Atritech Watchman™ or the Microvena PLAATO™ would be facilitated if a larger working channel could be made available.
Further reading related to the diagnosis and treatment of atrial fibrillation (AF) includes Hocini, M, et al., Techniques for Curative Treatment of Atrial Fibrillation, J. Cardiovasc Electrophysiol, 15(12): 1467-1471, 2004 and Pappone, C and Santinelli, V, The Who, What, Why, and How-to Guide for Circumferential Pulmonary Vein Ablation, J. Cardiovasc Electrophysiol, 15(10): 1226-1230, 2004. Further reading on RF ablation includes Chandrakantan, A, and Greenberg, M, Radiofrequency Catheter Ablation, eMedicine, topic 2957 Oct. 28, 2004. Further reading regarding catheter approaches to treating pathologies of the left atrium include Ross, et al, Transseptal Left Atrial Puncture; New Technique for the Measurement of Left Atrial Pressure in Man, Am J. Cardiol, 653-655, May 1959 and Changsheng M, et al., Transseptal Approach, an Indispensable Complement to Retrograde Aortic Approach for Radiofrequency Catheter Ablation of Left-Sided Accessory Pathways, J. H K Coll Cardiol, 3: 107-111, 1995.
A need, therefore, remains for improved access technology, which allows a device to be percutaneously or surgically introduced, endovascularly advanced to the right atrium, and enabled to cross the atrial septum by way of a myocardial puncture and Dotter-style follow-through. The device would further permit dilation of the myocardial puncture in the region of the atrial septum so that the sheath could pass relatively large diameter instruments or catheters, or multiple catheters through the same puncture. Such large dilations of the tissues of the atrial septum need to be performed in such a way that the residual defect is minimized when the device is removed. It would be beneficial if a cardiologist or hospital did not need to inventory and use a range of catheter diameters. It would be far more useful if one catheter or sheath diameter could fit the majority of patients or devices. Ideally, the catheter or sheath would be able to enter a vessel or body lumen with a diameter of 3 to 12 French or smaller, and be able to pass instruments through a central lumen that is 14 to 30 French. The sheath or catheter would be capable of gently dilating the atrial septum using radially outwardly directed force and of permitting the exchange of instrumentation therethrough without being removed from the body. The sheath or catheter would also be maximally visible under fluoroscopy and would be relatively inexpensive to manufacture. The sheath or catheter would be kink resistant, provide a stable or stiff platform for atrial septum penetration, and minimize abrasion and damage to instrumentation being passed therethrough. The sheath or catheter would further minimize the potential for injury to body lumen or cavity walls or surrounding structures. The sheath or catheter would further possess certain steering capabilities so that it could be negotiated through substantial curves or tortuosity and permit instrument movement within the sheath.